过热蒸汽流化床干燥装置

结合过热蒸汽干燥和流化床干燥的各自特性，开发出一种新型的过热蒸汽流化床干燥装置，阐述了工作原理。以卧式多室过热蒸汽流化床干燥装置干燥酒糟为例进行了工艺设计和计算，在保证稳定工作的条件下，干燥室内的绝对压力为0．3MPa，干燥室进出口的工作介质温度分别为180℃和140℃，最佳操作流化速度为2．6m／s。试验结果表明：该卧式多室过热蒸汽流化床干燥装置具有干燥速率大、热效率高、被干产品质量好和干燥操作成本低等优点，特别适宜于初始湿分高而加工附加值低的农产物料的干燥。     

过热蒸汽干燥技术的研究进展

过热蒸汽干燥技术具有安全、节能、环保等诸多优点,越来越受到广泛关注。对过热蒸汽干燥技术进行了简介,分析了其优缺点。总结了过热蒸汽干燥的理论研究进展,并对过热蒸汽干燥技术在食品、木材、纸张、污泥和和褐煤等物料的应用现状进行了综合评述。总而言之,过热蒸汽干燥技术是一种先进的干燥技术,具有广阔的应用前景。     

油页岩过热蒸汽的干燥动力学

以油页岩颗粒作为干燥物料,以过热蒸汽和热空气分别作为干燥介质,进行了油页岩干燥实验的研究。当颗粒粒径减小时,油页岩干燥速率越大;过热蒸汽和热空气温度增大时,干燥速率也越大。对比相同条件下过热蒸汽和热空气干燥油页岩的平均干燥速率,发现当干燥介质温度超过逆转点温度时,过热蒸汽条件下的平均干燥速率大于热空气下的数值。实验得出粒径分别为9,7,5 mm的油页岩颗粒逆转点温度值分别是154,179,177℃;逆转点温度值是个变量,随颗粒粒径大小变化而变化。颗粒粒径越大时逆转点温度值越小,粒径较小时逆转点变化不大。采用薄层干燥模型对油页岩的干燥数据进行动力学模拟,可得修正Page模型(Ⅱ)干基水分比w模拟值与实验值的最大绝对偏差是12%,综合比较发现修正Page模型(Ⅱ)能较好地描述油页岩在过热蒸汽条件下的干燥过程。     

过热蒸汽污泥干燥的机理与经济性分析

污泥产量增加且成分复杂,而传统的污泥干燥热效率低、能耗大,因此低能耗干燥方法是污泥干燥发展的重要方向。介绍了过热蒸汽干燥污泥的基础理论以及干燥特性,作了基本的经济分析计算,证明过热蒸汽干燥污泥存在巨大的优势,并提出了依据干燥机理提高污泥干燥速率、降低能耗的发展方向。     

过热蒸汽污泥干燥的机理与经济性分析

污泥产量增加且成分复杂,而传统的污泥干燥热效率低、能耗大,因此低能耗干燥方法是污泥干燥发展的重要方向。介绍了过热蒸汽干燥污泥的基础理论以及干燥特性,作了基本的经济分析计算,证明过热蒸汽干燥污泥存在巨大的优势,并提出了依据干燥机理提高污泥干燥速率、降低能耗的发展方向。     

软木干燥中湿空气和过热蒸汽的外部传热

In kiln drying of softwood timber, external heat and moisture mass transfer coefficients are important in defining boundary temperature and moisture content at the wood surface. In addition, superheated steam drying of wood is a promising technology but this has not been widely accepted commercially, partially due to the lack of understanding of the drying phenomena occurred during drying. In this work, experimental investigation was performed to quantify the heat transfer between wood surface and surrounding moist air or superheated steam. In the experiment, saturated radiata pine sapwood samples were dried using dry-bulb/wet-bulb temperatures of 60℃/50℃,90℃/60℃, 120℃/70℃, 140℃/90℃, 160℃/90℃, 140℃/100℃ and 160℃/100℃. The last two schedules were for superheated steam drying as the wet-bulb temperature was set at 100℃. The circulation velocity over the board surface was controlled at 4.2 m·s-1. Two additional runs (90℃/60℃) using air velocities of 2.4 m·s-1 and 4.8 m·s-1were performed to check the effect of the circulation velocity. During drying, sample weight and temperatures at wood surface and different depths were continuously measured. From these measurements, changes in wood temperature and moisture content were calculated and external heat-transfer coefficient was determined for both the moist air and the superheated steam drying.     

过热蒸汽携湿在褐煤干燥中的应用

通过调整过热蒸汽温度与流量,得到了理想的褐煤产品,并确定了最佳的携湿参数,为褐煤干燥携湿技术提供了理论依据。     

耦合过热蒸汽干燥的MVR蒸发结晶系统热力性能分析

机械蒸汽再压缩（MVR）作为目前最先进的蒸发结晶技术得到广泛关注和应用,本文结合过热蒸汽干燥技术的优势,提出一种耦合过热蒸汽干燥的MVR蒸发结晶干燥系统。基于EES软件建立数值模型,通过系统仿真的方法分析闪蒸压力p_flash、进料浓度c₀、循环倍率CR、换热温差ΔT_mhex等对压缩机能耗W_comp和系统能效系数COP、下降管结晶盐含水率的上限值ω和换热器UA值的影响情况。结果表明：耦合过热蒸汽干燥的MVR系统相比常规系统具有更高的COP、更低的W_comp,并且能够获得干燥的结晶盐;循环倍率CR增大,压缩机压比π降低,有利于提高COP和降低W_comp,但同时换热器UA_mhex值会增大,设备成本增加;系统COP随p_flash的变化关系与循环倍率CR有关,CR较低时,随P_flash的增大,系统COP增大,CR超过某一定值,随着p_flash的增大,系统COP呈先升后降趋势,其最大值在p_flash为40~50kPa;进入干燥器的下降管结晶盐含水率的上限值ω与进料浓度c₀有关,随进料浓度c₀的升高而增大;?T_mhex对MVR系统性能有显著的影响,?T_mhex每增大1K,COP平均降低5.6%、W_comp平均升高5.8%、UA_mhex平均减少14.4%,ω平均升高1.7%。     

利用蒸汽喷射装置回收糟液余热

用蒸汽为动力，通过蒸汽喷射泵把从粗馏塔中排出的糟液中的余热闪蒸出来，作为粗馏塔的热源，该装置投用后，年节约30.9万元。     

过热蒸汽流化床制备粒状磷酸一铵的实验研究

实验研究了过热蒸汽流化床反应干燥一步法制备粒状MAP的工艺条件,在70 kPa,100～130℃,进料n(NH3)/n(H3PO4)为1.2～1.6条件下,床层操作稳定,制得了性状良好的球形磷酸一铵产品。     

Drying paper by impinging jets of superheated steam. Part 1: Constant drying rate in superheated steam

Over a wide range of operating conditions, the drying of paper by impinging jets of superheated steam proceeds by a constant rate period followed by a falling rate period. The constant drying rate, investigated here in the jet temperature range 150 ≤ T_j/ ≤ 465°C and over jet Reynolds numbers of 1000 ≤ Re_j ≤ 12000, is predicted within + 12% by a heat transfer expression using Martin's (1977) correlation for the heat transfer coefficient corrected for mass transfer by the Couette flow approximation factor, and a property ratio to account for the large temperature difference between the jet and the paper.     

Discrete pore network modeling of superheated steam drying

A nonisothermal two-dimensional pore network model is developed to describe the superheated steam drying of a capillary porous medium. The complex void space is approximated by a network of spherical pores interconnected by cylindrical throats. In this model, the condensation of water vapor at the network surface as well as the network drying are taken into account. During the network drying period, the liquid transport is driven by capillary action, whereas vapor transport occurs because of convection. The condensation of water vapor within the pores is modeled based on newly formulated liquid invasion rules. The simulation results, presented as temperature and moisture content profiles over time, indicate qualitative agreement with available experimental observations. The inclusion of the liquid invasion rules is shown to accommodate more of the condensed water mass compared to earlier models, in which condensation is only partly treated. Due to the viscous vapor flow, the vapor overpressure within the network, which is the driving force of vapor transport, is reproduced in these simulations. The influence of vapor overpressure on the disintegration of the liquid phase is also discussed.     

Comparative study of moisture absorption and dimensional stability of Chinese cedar wood with conventional drying and superheated steam drying

The effects of drying methods on equilibrated moisture content (MC) and swelling efficiency of Chinese cedar (Cryptomeria fortunei) wood were studied in this paper. Drying experiments were conducted with conventional (CON) drying and superheated steam (SHS) drying under atmospheric pressure. Specimens were equilibrated at two environment conditions to measure moisture and dimensional changes, and then the moisture excluding efficiency (MEE) and antiswelling efficiency (ASE) were determined. Results showed that the equilibrated MC of artificial-dried wood was lower than control samples (air drying), and the equilibrated MC of wood with SHS drying was lower than that with CON drying, which indicated that MEE was enhanced in SHS drying process. Similar results were found in swelling efficiency and ASE of artificial-dried wood and the control. The mechanism was studied by dynamic mechanical analysis (DMA) and X-ray diffraction analysis (XRD). The DMA results showed that both of relative storage modulus and relative loss modulus were the highest for SHS-dried wood and the lowest for the control samples. As for the crystalline structure assessed by changes of XRD, the results showed that the cellulose crystallinity and crystallite size of Chinese cedar wood with SHS drying were the highest, and control specimens were the lowest. All the analyses showed that Chinese cedar wood with low hygroscopic and high dimensional stability could be gotten through SHS drying process.     

Reducing energy requirement for drying of beet-pulp: Simulation of energy integration between superheated steam and air drying systems

Beet-pulp dehydration in the sugar industry is a highly energy intensive unit operation. Producing 1?kg of dried beet-pulp requires ～2–3?kg of water to be removed. The cost saving is a real challenge in sugar factory as the current dryers are underperforming (around 3?MJ/kg of water evaporated) because the heat recovery is limited and only a small proportion of dryer exhaust can be reused. The aim of this study was to investigate by simulation the energy efficiency of an independent multistage drying method that combines superheated steam drying (SHSD) and hot air drying (AD). Two case studies awarding the two types of energy coupling (AD then SHSD or SHSD then AD) are presented and compared. An approach of optimization is developed from energy balance. A number of operating parameters of the two drying configurations are investigated using sensitivity analysis. It proves that both cases allow an energy economy around 40% compared to the conventional dryer. Nevertheless, the SHSD-AD plant may present more benefits for a better quality product.     

Convective drying of wood-waste in air and superheated steam

The convective batch drying of Western Hemlock hog fuel-sized particles in fixed beds under various operating conditions quantiatively established the effect of factors which govern the drying process. A correlation was obtained for the Nusselt number during the heat transfer controlled period. Under specific conditions, the existence of a unified characteristic drying rate curve was confirmed. Drying behaviour as described by the receding plane model provided a mathematical expression for such a curve. The existence of an inversion point temperature was experimentally confirmed.     

Drying of soy sauce residue in superheated steam at atmospheric pressure

Soy sauce residue needs drying to avoid fermentation and oxidation during storage and transportation, and its reutilization as a useful resource is expected. Superheated steam drying was applied to investigate the effects of drying conditions on the drying characteristics and the content changes of salt and protein. The results showed that the inversion temperature was about 130°C, beyond which superheated steam drying was faster than hot air-drying. The drying time approaching equilibrium moisture content was reduced with elevated drying temperature as well as higher steam mass flow rate in the present experimental conditions. The effect of bed thickness on drying time was not obvious when drying temperature increased. Interestingly, the salt content of soy sauce residue could be decreased by 34.8% due to condensate water in the initial drying period (wetting), while protein content had no significant loss (p?相似文献   

Newly designed superheated steam dryer bearing heat recovery unit: Analysis of energy efficiency and kinetics of Kelp drying

In this work, a newly designed superheated steam dryer (SSD) bearing exhaust heat recovery unit (RD) was fabricated. The dryer was designed for the superheated steam (SS) to be generated by foodstuff being dried, and the latent heat of the exhaust SS was recovered by microtube radiators and exploited to heat the RD unit. The system was then applied in Kelp drying, in which the drying kinetics was analyzed and fitted with mathematical models. The energy efficiency by the system was further evaluated and compared with hot air (HA)-drying. The results showed that the Kelp drying process in SSD could be described by two stages: heat-upstage (stage I) and superheated steam stage (stage II). While in stage I, different heat-up times of 10, 15, and 20?min were required to generate superheated steam at temperatures of 110–150°C, in stage II, the moisture content in Kelp was decreased to approximately 50?±?5% (wet basis) within 60, 50, and 30?min at 110, 130, and 150°C, respectively. Moreover, the Midilli and Kucuk model best described Kelp drying curve in both stages, whereas the logarithmic model best fitted with that in stage II. Finally, the energy efficiency for SSD-RD was in the range of 1.127–1.425?kWh/kg_water compared with 2.406–2.508?kWh/kg_water for HA operating under the same conditions, demonstrating that the SSD-RD was able to reduce the energy input by at least 46.14%.     

过热蒸汽袋式除尘器阻力特性研究

过热蒸汽与高温、高湿烟气具有相似的特性,针对高温、高湿烟气袋除尘困难的问题,设计开发了过热蒸汽袋式除尘器,并试验分析了气体参数对其阻力的影响.结果表明,过热蒸汽袋式除尘器运行状况良好,除尘器阻力随进口气体温度的升高及蒸汽通入时间的延长呈"鱼钩曲线"变化;而蒸汽过热度增加,除尘器阻力减小.     

Evaluation of the energy efficiency of combined drying and heat treatment by superheated steam

This study compares energy efficiency of a combined drying and heat treatment with that of conventional hot air heat treatment, the theoretical heat consumptions required for each treatment were determined, and the actual heat consumptions for each treatment were measured at a pilot scale. Conventional heat treatment method separately performs kiln-drying and heat treatment for wood with hot air in different equipment. On the contrary, in the combined treatment, the wood is simultaneously dried and heat-treated in the same enclosed space. Because of the time and energy savings, the economic feasibility of combined treatment is much higher than that of conventional heat treatment. Although the theoretical required energy of the combined treatment was similar to that of the two-stage method, the actual energy consumption of combined treatment was less than that of the two-stage method. And, the energy efficiency of the combined treatment was calculated to be two times higher than that of the two-stage method. From the results of this study, decreases in the processing time and energy consumption and increases in the energy efficiency of the combined treatment by superheated steam were quantitatively shown when compared to two-stage method.